An electronic apparatus such as a digital video electronic device or a digital still electronic device includes a solid-state imaging device such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Silicon Transistor) image sensor.
In the solid-state imaging device, a plurality of pixels is arranged on a semiconductor substrate in a matrix shape in horizontal and vertical directions. Further, a light receiving surface is formed on the semiconductor substrate. In the light receiving surface, for example, a sensor which is a photoelectric converting section such as a photodiode is installed for each pixel.
On the light receiving surface is formed a light concentrating structure which concentrates light by a subject image into the sensor for each pixel. Here, the light concentrating structure receives the light by the subject image and photo-electrically converts the received light to generate signal electric charge, thereby obtaining a pixel signal.
In the CCD or CMOS image sensor in the related art, the light incident to the sensor section is photo-electrically converted by the photodiode, so that the incident light is converted into electric charge to obtain an image signal. Such a device has a structure in which the light is incident for a specific exposure time to be converted into the electric charge and accumulated.
Since the amount of the accumulated electric charge is finite, for example, when the incident light is strong, the electric charge is saturated, so that the grayscale of white and black becomes insufficient. That is, the solid-state imaging device has an incident light amount range for obtaining an appropriate output signal, however the range is remarkably narrow compared with an image pickup target.
Thus, it is desirable to provide a technique which enlarges a dynamic range of a solid-state imaging device.
As a technique of enlarging the dynamic range in the related art, “2005 IEEE Workshop on Charge-Coupled Devices and Advanced Image Sensors P.169, P.173” discloses a technique which changes increments of the photoelectric conversion according to the incident light amount. Further, JP-A-2008-167004 discloses a method which sets a gain according to the incident light amount.
Further, JP-A-2006-333439 discloses a solid-state imaging device including a light blocking member which blocks a photoelectric converting section, and an actuator which drives the light blocking member using MEMS.
In addition to these techniques which attempt to enlarge the dynamic range with the device configuration, there are proposed techniques which enlarge the dynamic range using materials.
For example, JP-A-1-75602 and JP-A-9-129859 disclose devices in which an electrochromic material is provided on a package.
Further, JP-A-8-294059 discloses a device in which an electrochromic material is provided over an entire surface of pixels and transmittance is controlled for each pixel.
Further, JP-A-2008-124941 discloses a technique in which an electrochromic material is provided in a pixel area to change transmittance, so as to change the transmittance of visible light and near infrared light.
Further, in view of transmittance control, JP-A-11-234575 discloses a technique in which an accumulation time is variable to increase an apparent dynamic range.
JP-A-2001-352490 discloses a technique which repeatedly reads signals of long and short exposure times to increase the dynamic range.
JP-A-2007-329721 discloses a technique which combines a plurality of signals having different sensitivity for each pixel to enlarge the dynamic range.
For example, in the techniques which enlarge the dynamic range in signal processing using a high sensitivity signal and a low sensitivity signal, as disclosed in JP-A-11-234575, JP-A-2001-352490 and JP-A-2007-329721, as an accumulation time difference is used to obtain the high sensitivity signal and the low sensitivity signal, an image of a moving subject becomes unnatural.
Further, in the technique which employs an ND filter, as disclosed in JP-A-2008-124941, the enlargement factor of the dynamic range is difficult to be changed.
In JP-A-8-294059, a method is disclosed in which the transmittance of the electrochromic material is adjusted by feeding back a pixel output signal for each pixel. According to this technique, the above problems can be solved.
However, in this case, since the time when voltage can be applied to the electrochromic material of each pixel is only time corresponding to the data rate, it is necessary to enhance a frequency characteristic of a feedback system to such a degree. Thus, it is difficult to realize the device. Even if the device can be realized, power consumption becomes increased.